Method of manufacturing dynamic pressure bearing member

Abstract

A method of manufacturing dynamic pressure bearing member is provided. A method of manufacturing a dynamic pressure bearing member, by providing a metal mold die including a core pin provided with protruding stripes of a predetermined shape formed on an outer peripheral surface for forming dynamic pressure grooves, and injecting molten resin in the metal mold die to form at least a series of dynamic pressure grooves on an inner peripheral surface with a circular cross-section in an inner circumferential direction, includes the step of pulling out in a forced pullout manner one of the core pin from the dynamic pressure bearing member or the dynamic pressure bearing member from the core pin in an axial direction of the dynamic pressure bearing member after curing the molten resin, in a condition in which a free space is provided around an outer periphery of the molded dynamic pressure bearing member.

1 . A method of manufacturing a dynamic pressure bearing member, by providing a metal mold die including a core pin provided with protruding stripes of a predetermined shape formed on an outer peripheral surface for forming dynamic pressure grooves, and injecting molten resin in the metal mold die to form at least a series of dynamic pressure grooves on an inner peripheral surface with a circular cross-section in an inner circumferential direction, comprising: 
 pulling out in a forced pullout manner one of the core pin from the dynamic pressure bearing member or the dynamic pressure bearing member from the core pin in an axial direction of the dynamic pressure bearing member after curing the molten resin, in a condition in which a free space is provided around an outer periphery of the molded dynamic pressure bearing member.    
   
   
       2 . The method of manufacturing a dynamic pressure bearing member according to  claim 1 , 
 wherein corners of the protruding stripes formed on the outer peripheral surface of the core pin are chamfered.    
   
   
       3 . The method of manufacturing a dynamic pressure bearing member according to  claim 1 , 
 wherein the protruding stripes are formed so that a shape of a cross-section of each of the protruding stripes formed on the outer peripheral surface of the core pin forms an acute angle with the reference of the outer peripheral surface of the core pin to a direction of the forced pullout of the dynamic pressure bearing member, and the acute angle is in a range of 30° through 45°.    
   
   
       4 . The method of manufacturing a dynamic pressure bearing member according to  claim 1 , 
 wherein the cross-sectional shapes corresponding to the shapes of the dynamic pressure grooves are formed on the outer peripheral surface of the core pin as trapezoidal protruding stripes, a tilt angle of at least a rear slope of the trapezoidal protruding stripes in the forced pullout direction is formed as an acute angle with the reference of the outer peripheral surface of the core pin, the acute angle is formed in a range of 30° through 45°, and the surface corner sections of each of the trapezoidal protruding stripes and the base sections of each of the trapezoidal protruding stripes are chamfered or formed as substantially round corners.    
   
   
       5 . The method of manufacturing a dynamic pressure bearing member according to  claim 1 , 
 wherein the cross-sectional shapes corresponding to the shapes of the dynamic pressure grooves are formed on the outer peripheral surface of the core pin as partial circular protruding stripes, the base sections of each of the partial circular protruding stripes are chamfered or formed as substantially round corners.    
   
   
       6 . The method of manufacturing a dynamic pressure bearing member according to  claim 1 , 
 wherein the core pin is rotated, and the core pin is pulled out in a forced pullout manner in the axial direction of the dynamic pressure bearing member in the condition in which the free space is provided around the dynamic pressure bearing member.    
   
   
       7 . A method of manufacturing a dynamic pressure bearing member provided with at least a series of dynamic pressure grooves formed on an inner peripheral surface with a circular cross-section in the inner circumferential direction by injection molding, comprising: 
 providing an injection molding die including    a fixed part die provided with a molten resin injection gate formed adjacent to a parting surface,    a movable part die provided with a parting surface capable of adhering to the parting surface of the fixed part die, a through hole with a circular cross-section penetrating to the parting surface, and a cavity forming at least a part of the dynamic pressure bearing member to be formed, and    a core pin having a thickness capable of being inserted in the through hole of the movable part die, facing at least the cavity, and provided with protruding stripes of predetermined shapes formed on the outer peripheral surface, for forming the dynamic pressure grooves;    fastening the parting surface of the movable part die to the parting surface of the fixed part die after abutting the parting surface of the movable part die on the parting surface of the fixed part die and adhering the parting surface of the movable part die to the parting surface of the fixed part die in the condition in which the core pin is inserted to a predetermined position of the through hole of the movable part die;    filling the cavity formed of the fixed part die and the movable part die with the molten resin by injecting the molten resin into the cavity from the molten resin injection gate;    releasing the fastening between the fixed part die and the movable part die after the injected and filled molten resin has been cured;    moving the movable part die backward from the parting surface of the fixed part die and an outer peripheral surface of the cured dynamic pressure bearing member; and    subsequently pulling out in a forced pullout manner one of the core pin from the dynamic pressure bearing member or the dynamic pressure bearing member in an axial direction of the dynamic pressure bearing member, in a condition in which the movable part die does not exist around the dynamic pressure bearing member.    
   
   
       8 . The method of manufacturing a dynamic pressure bearing member according to  claim 7 , 
 wherein the protruding stripes on the outer peripheral surface of the core pin are formed in two or more columns with a predetermined interval in the axial direction of the core pin.    
   
   
       9 . The method of manufacturing a dynamic pressure bearing member according to  claim 8 , 
 wherein the protruding stripes on the outer peripheral surface of the core pin are V-shaped protrusions provided in series.    
   
   
       10 . The method of manufacturing a dynamic pressure bearing member according to  claim 9 , 
 wherein the core pin is rotated, and the core pin is pulled out in a forced pullout manner in the axial direction of the dynamic pressure bearing member in the condition in which the free space is provided around the dynamic pressure bearing member.    
   
   
       11 . The method of manufacturing a dynamic pressure bearing member according to  claim 10 , 
 wherein the rotational direction of the core pin is a direction towards the extremity of the V-shaped protruding stripes.    
   
   
       12 . The method of manufacturing a dynamic pressure bearing member according to  claim 11 , 
 wherein in the case in which the core pin is pulled out in a forced pullout manner in the axial direction of the dynamic pressure bearing member provided with the dynamic pressure grooves formed on the inner peripheral surface of the cylindrical section in two or more columns,    the rotational angle of the core pin excludes an angle with which the series of protruding stripes drop in the adjacent dynamic pressure grooves in the axial direction in which the core pin is pulled out in a forced pullout manner.    
   
   
       13 . The method of manufacturing a dynamic pressure bearing member according to  claim 9 , 
 wherein corners of the protruding stripes formed on the outer peripheral surface of the core pin are chamfered.    
   
   
       14 . The method of manufacturing a dynamic pressure bearing member according to  claim 9 , 
 wherein the protruding stripes are formed so that a shape of a cross-section of each of the protruding stripes formed on the outer peripheral surface of the core pin forms an acute angle with the reference of the outer peripheral surface of the core pin to a direction of the forced pullout of the dynamic pressure bearing member, and the acute angle is in a range of 30° through 45°.    
   
   
       15 . The method of manufacturing a dynamic pressure bearing member according to  claim 9 , 
 wherein the cross-sectional shapes corresponding to the shapes of the dynamic pressure grooves are formed on the outer peripheral surface of the core pin as trapezoidal protruding stripes,    a tilt angle of at least a rear slope of the trapezoidal protruding stripes in the forced pullout direction is formed as an acute angle with the reference of the outer peripheral surface of the core pin, the acute angle is formed in a range of 30° through 45°, and    the surface corner sections of each of the trapezoidal protruding stripes and the base sections of each of the trapezoidal protruding stripes are chamfered or formed as substantially round corners.    
   
   
       16 . The method of manufacturing a dynamic pressure bearing member according to  claim 9 , 
 wherein the cross-sectional shapes corresponding to the shapes of the dynamic pressure grooves are formed on the outer peripheral surface of the core pin as partial circular protruding stripes, and    the base sections of each of the partial circular protruding stripes are chamfered or formed as substantially round corners.